Question about plaster wall repair and painter

[Anonymous]

We just hired a painter who came recommended and who has been in the business for over 30 years. We hired him to repair water damage to the walls from a leaky roof and to paint the rooms. After coming to give us an estimate he said the job was a small one and could be done in one day. Does this sound right? He said he used a 5 minuet setting plaster which would allow for the same day painting. Anyone familiar with this process. Also, if we want to paint the same color do we need a separate primer? Any other advice on what I should make sure we are clear prior to signing the contract would be appreciated.